The present invention relates to a pneumatic tire and more particularly to a pneumatic tire having a combination of driving stability with riding comfort by virtue of an improvement in the tread pattern.
It is known that the tread rigidity of a tire greatly influences the driving stability and the riding comfort. There is an antinomic relationship between the driving stability and the riding comfort, which has made it very difficult to attain a combination of both the performances. Specifically, an increase in the tread rigidity brings about an increase in the cornering power, which contributes to an improvement in the driving stability of the tire. However, this brings about an increase in the impact force applied to the tread surface, so that the riding comfort is lowered. The tread rigidity can be relatively easily altered by changing a pattern comprising ribs and blocks formed on the tread surface.
In the cornering of a vehicle, the angle of the direction of the advance of the vehicle relative to the circumferential direction of the deflected tire is called a "slip angle". In usual cornering of a general passenger car, as shown in FIG. 6, the slip angle .theta. of the tire is usually about 1.degree.. From this point of view, as shown in FIG. 5, the tread pattern of the conventional tire for a passenger car generally comprises a rib 1 provided on the equatorial line (EL) of the tire and, provided in rows on the both sides thereof, a plurality of blocks 5 partitioned by main grooves 3 and subgrooves 4. However, the tire having this type of center rib brings about an increase in the cornering force at a slip angle as small as about 1.degree., which ensures the driving stability. However, since the rigidity of the center portion of the tire is large, the riding comfort is unfavorably poor.